943 research outputs found
Biodiesel Produced from Catalyzed Transesterification of Triglycerides Using ion-Exchanged Zeolite Beta and MCM-22
AbstractIn this work, biodiesel production from catalyzed transesterification of triglycerides with excess methanol was studied by using ion-exchanged Zeolite Beta and MCM-22 as heterogeneous catalysts. Zeolite Beta and MCM-22 were synthesized with hydrothermal processes and, subsequently, modified by ion-exchanged with alkali ions. These as-obtained zeolite catalysts could yield a high conversion of triglycerides to biodiesel. The conversion efficiency was largely affected by crystallinity and frameworks of zeolite support, pH value of alkali ion-exchange solutions and alkali loadings onto the zeolite support. Furthermore, the effects of the duration of the sodium ion-exchange process on the final conversion efficiency of triolein to biodiesel, both the as-prepared Zeolite MCM-22 and Zeolite Beta catalysts were used. The effect of the duration of the sodium ion-exchange process is insignificant in transesterification using Na-ion-exchanged Zeolite MCM-22 catalysts from 0.5 to 4h. In contrast, the conversion efficiency of triolein to biodiesel reached ca. 95% in 0.5hours of transesterification using Zeolite Beta ion-exchanged with 3 mmol-eq. Na+/g cat for 0.5hours
Hawking Radiation Under Generalized Uncertainty Principle
The generalized uncertainty relation is expected to be an essential element
in a theory of quantum gravity. In this work, we examine its effect on the
Hawking radiation of a Schwarzschild black hole formed from collapse by
incorporating a minimal uncertainty length scale into the radial coordinate of
the background. This is implemented in both the ingoing Vaidya coordinates and
a family of freely falling coordinates. We find that, regardless of the choice
of the coordinate system, Hawking radiation is turned off at around the
scrambling time. Interestingly, this phenomenon occurs while the Hawking
temperature remains largely unmodified.Comment: 23 pages, 1 figur
UV Dispersive Effects on Hawking Radiation
We revisit the connection between Hawking radiation and high-frequency
dispersions for a Schwarzschild black hole following the work of Brout et al..
After confirming the robustness of Hawking radiation for monotonic dispersion
relations, we consider non-monotonic dispersion relations that deviate from the
standard relation only in the trans-Planckian domain. Contrary to the common
belief that Hawking radiation is insensitive to UV physics, it turns out that
Hawking radiation is subject to significant modifications after the scrambling
time. Depending on the UV physics at the singularity, the amplitude of Hawking
radiation could diminish after the scrambling time, while the Hawking
temperature remains the same. Our finding is thus not contradictory to earlier
works regarding the robustness of Hawking temperature.Comment: 24 pages, 8 figure
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